Milestone Electronics
USB to RS232/ RS422/ RS485 (isolated)
The UD-2535U enables high-speed isolated data transmission between a computer USB port and RS422, RS485, or RS232 devices over long distances under high electrical noise conditions.
- USB 2.0 compliant input with RS422, RS485, and RS232 output interfaces on a single unit
- Opto-isolated signal lines with spike suppression for protection against electrical noise and transients
- 4-wire full duplex and 2-wire half duplex mode selection via front-panel slide switch
- Bus-powered through USB cable with optional 5V adaptor support
- 7-pin Phonex connector output with shielded CAT5 cable on RS422 / RS485 side
Max Resolution
1080p Full HD
Audio Input
Stereo Analogue
Output
Single HDMI
- In-house manufactured
- 24hr response
- 2,000+ clients served
Product Overview
What makes the UD-2535U
The UD-2535U is a USB to RS422 / RS485 / RS232 converter designed for high-speed isolated data transmission between a computer USB port and external peripherals or devices equipped with RS422, RS485, or RS232 interfaces. It is built for use over long distances and in environments with elevated electrical noise, making it well suited to demanding industrial and field installations.
The converter provides opto-isolation and spike suppression on each signal line, protecting the connected devices from electrical transients and common mode interference. The use of shielded twisted-pair CAT5 cable on the RS422 / RS485 side, combined with the differential signalling inherent to RS422 and RS485, provides high common mode noise rejection across cable runs.
A front-panel slide switch allows the user to select between 4-wire full duplex mode for RS422 / RS485 applications and 2-wire half duplex mode, enabling compatibility with a wide range of industrial devices and control systems. Three front-panel LED indicators for Power, Transmit Data, and Receive Data provide real-time communication status.
The unit includes a 7-pin Phonex output connector that carries all RS422 / RS485 and RS232 signals. It draws power directly from the USB cable, making it fully bus-powered without requiring an external supply in standard deployments. An optional 5V adaptor can be used when additional power margin is required.
Input Interface
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Key Features
Built for reliable long-distance serial communication
USB to RS422, RS485, and RS232 on one unit. Opto-isolated, bus-powered, and field-ready for industrial environments where noise immunity and signal integrity matter.
Triple Interface Output
A single unit provides simultaneous access to RS422, RS485, and RS232 output interfaces, eliminating the need for separate converters for different device types.
- RS422 / RS485 on Tx+, Tx-, Rx+, Rx- lines
- RS232 on dedicated Tx, Rx, and GND pins
- All signals accessible via 7-pin Phonex connector
Opto-Isolation and Spike Suppression
Each signal line is protected with opto-isolation and spike suppression, preventing damage from electrical transients and ground potential differences common in industrial installations.
- Opto-isolation on every signal line
- Spike suppressor protects against voltage transients
- High common mode noise rejection via differential signalling
Selectable 4-Wire and 2-Wire Modes
A front-panel 2-way slide switch allows the user to select between 4-wire full duplex operation for RS422 / RS485 and 2-wire half duplex mode, providing compatibility with diverse field devices.
- 4-wire mode for full duplex RS422 / RS485 communication
- 2-wire mode for half duplex RS485 bus configurations
- Mode selection without tools or software
USB 2.0 Compliant Input
The unit connects to the PC via a standard USB A-A cable and is fully USB 2.0 compliant, presenting itself as a Virtual COM Port after driver installation for compatibility with standard serial software.
- USB 2.0 compliant interface
- Virtual COM Port driver creates a standard serial port
- Configurable baud rate and buffer size via device manager
Front Panel LED Indicators
Three clearly labelled LED indicators on the front panel provide immediate visual feedback on unit power status and live data activity on transmit and receive lines.
- Power LED confirms unit is receiving power
- TD LED indicates transmit data activity on RS485 / RS232
- RD LED indicates receive data activity on RS485 / RS232
Bus-Powered with Optional Adaptor
The converter draws its operating power directly from the USB port, requiring no external power supply for standard use. An optional 5V / 1A adaptor is available for installations where a USB power source may not be available.
- Powered through USB cable in standard operation
- Optional 5V / 1A adaptor for non-USB power environments
- Compact 105 x 75 x 32mm form factor
Installation
Driver installation and wiring for the UD-2535U
The UD-2535U installs on a PC via USB and is recognised as a Virtual COM Port after driver setup. Cable wiring follows standard RS422 / RS485 twisted-pair practices for reliable long-distance communication.
01
Connect and Install Driver
Plug the UD-2535U into the PC USB port using the supplied USB A-A cable. Windows will attempt automatic driver installation. Insert the supplied CD or download the UD25 Driver from www.milestone.co.in, which includes the Virtual COM Port Driver and USB Bridge. Follow the on-screen steps until the message "MLU485 installed successfully" is displayed and click OK. This installation is required only once or after uninstallation.
02
Verify Virtual COM Port
After driver installation, open Windows Device Manager and confirm that the Virtual COM Port has been created. Check the port properties to set the required baud rate and buffer size for the target device. The unit is now ready for serial communication between the PC and the connected RS232, RS422, or RS485 device using the assigned COM port.
03
Select Duplex Mode and Connect Cable
Use the front-panel slide switch to select 4-wire mode for full duplex RS422 / RS485 or 2-wire mode for half duplex RS485 communication. Connect the RS422 / RS485 device using a shielded twisted-pair CAT5 cable. For 4-wire configurations, connect -Rx to -Tx and +Rx to +Tx at the instrument end. For 2-wire configurations, connect +Tx / +Rx and -Tx / -Rx straight across. For RS232 use, connect to pins 6 and 7 of the Phonex connector.
04
Long Distance Cable Laying Guidelines
Use a twisted-pair cable such as CAT5 for all long-distance RS422 / RS485 runs. Each signal pair uses the plus and minus conductors of a single twisted pair to maximise common mode noise rejection. Do not run the signal cable parallel to power line cables. Ensure cable resistance does not exceed 90 ohms per 1000 metres. Route the cable through conduit pipe for physical protection in exposed environments.
Where the UD-2535U performs
Designed for environments that demand reliable USB to serial connectivity with isolation, spanning factory floors, access control systems, data collection setups, and remote terminal installations.
Factory Automation
Connects PCs to RS485-based automation devices, PLCs, and field controllers over extended cable runs in industrial environments where electrical noise levels are high.
Programmable Logic Controllers
Interfaces directly with PLC RS232 and RS485 ports, enabling configuration, monitoring, and data exchange from a connected PC without additional converter hardware.
Attendance Recording Systems
Provides reliable USB to RS485 connectivity for time and attendance terminals that communicate over multi-drop RS485 networks in corporate or institutional environments.
Barcode Readers
Connects RS232-based barcode readers to modern PCs via USB, enabling point-of-sale, inventory management, and logistics systems to use legacy scanner hardware.
Remote Data Transmission
Enables data transfer between PC systems and RS422 / RS485 devices across long cable distances, supported by the differential signal format and shielded CAT5 wiring recommendations.
EPABX and Remote Terminals
Connects RS232 remote terminals and EPABX equipment to a PC via USB, supporting legacy serial communication in telephony infrastructure and building management systems.
Full specification sheet
- Input Interface
- Output Interface
- Connector Pin Assignment
- Protection
- Mode Selection
- Indicators
- Power
- Physical
- Kit Contents
- Cable Laying Guidelines
FAQs about the UD-2535U
What is the purpose of the UD-2535U?
The UD-2535U is a USB to RS422 / RS485 / RS232 converter that allows a PC to communicate with industrial and serial devices over its USB port. It is designed for high-speed, isolated data transmission over long distances in environments with high electrical noise, such as factory floors, building automation systems, and industrial control installations.
How is the UD-2535U installed on a Windows PC?
Plug the unit into the PC USB port using the supplied USB A-A cable. Insert the supplied CD or download the UD25 Driver from www.milestone.co.in. Follow the installation steps until the message “MLU485 installed successfully” appears and click OK. Then verify in Windows Device Manager that the Virtual COM Port has been created and configure the baud rate and buffer settings as required. This installation is needed only once or after driver removal.
What is the difference between 4-wire and 2-wire mode?
4-wire mode enables full duplex RS422 / RS485 communication, where transmit and receive signals are carried on separate pairs, allowing simultaneous bidirectional data flow. 2-wire mode configures the unit for half duplex RS485 operation, where a single pair is shared for both transmit and receive, and only one device can transmit at a time. The mode is selected using the slide switch on the left side panel of the unit.
How does the opto-isolation protect connected equipment?
Opto-isolation electrically separates the USB side of the converter from the RS422 / RS485 / RS232 output side. This prevents ground loops and protects the PC and connected devices from voltage differences and electrical transients that are common in industrial environments. A spike suppressor on each signal line provides additional protection against voltage spikes that could otherwise damage the converter or the connected equipment.
What cable should be used for long-distance RS422 / RS485 runs?
A shielded twisted-pair cable such as standard CAT5 is recommended for all RS422 / RS485 long-distance runs. Each signal pair, the plus and minus conductors of a single twisted pair, should be used to carry one differential signal, which maximises common mode noise rejection. The cable should not be routed parallel to power line cables, the resistance should not exceed 90 ohms per 1000 metres, and the cable should pass through conduit pipe for physical protection.
Does the UD-2535U require an external power supply?
No. The UD-2535U is bus-powered and draws its operating power directly from the USB cable connected to the PC. An external power supply is not required for standard installations. However, an optional 5V / 1A adaptor is available for deployments where a USB power source is not accessible or where additional power headroom is needed.
How do I uninstall the UD-2535U driver?
To uninstall the driver, run the CYG_UNINSTALL utility from the supplied CD. A screen will guide you through the removal process. After uninstallation is complete, the Virtual COM Port will be removed from Device Manager. The driver can be reinstalled at any time using the same CD or by downloading the UD25 Driver package from www.milestone.co.in.
Can the UD-2535U connect to both RS232 and RS485 devices at the same time?
The UD-2535U provides RS422 / RS485 and RS232 signal lines on different pins of the same 7-pin Phonex output connector. The RS422 / RS485 signals are on pins 1 through 5 and the RS232 Tx and Rx lines are on pins 6 and 7, with GND shared on pin 3. Whether signals from multiple interfaces can be used simultaneously depends on the connected devices and the application software. For most deployments, the unit is connected to one interface type at a time using the appropriate wiring for that interface.
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